Referring to FIGS. 1 to 3, a pump head 1 disclosed in U.S. Pat. No. 5,762,095 for connecting an air supply source 11 and an air valve 12 is shown. The pump head 1 includes a cylindrical body 131, two spaced-apart flanges 132 extending upwardly from the cylindrical body 131, a slot 133 formed between the flanges 132, and a lateral hollow arm 134 projecting from the cylindrical body 131 for connecting the air supply resource 11. The cylindrical body 131 has an open end 130, and a chamber 135 communicated with the slot 133. A cam lever 15 is pivotally disposed in the slot 133 through a pivotal pin 60. A coupler unit 16 is disposed in the chamber 135. An end cap 17 is connected to the open end 130.
The cam lever 15 includes cam head 151 for insertion of the pivotal pin 14, and a handle 152 extending outwardly from the slot 133. The cam head 151 has a first engagement surface 153 and a second engagement surface 154 perpendicular to the first engagement surface 153. A distance between the first engagement surface 153 and the pivotal pin 14 is smaller than a distance between the second engagement surface 154 and the pivotal pin 14. The coupler unit 16 includes a plug 161 abutting the cam head 151, a deformable tightening ring 162 spaced apart from the plug 161, and a spacer 163 abutting between the plug 161 and the tightening ring 162.
As shown in FIGS. 1 and 2, when the pump head 1 is in an initial state, the first engagement surface 153 abuts the plug 161 of the coupler tightening unit 16, and the air valve 12 can extend into the end cap 17, the tightening ring 162 and the spacer 163. When the cam lever 15 is rotated about the pivotal pin 14, the second engagement surface 154 abuts against the plug 161 (see FIG. 3). Because the distance between the second engagement surface 154 and the pivotal pin 14 is greater than the distance between the first engagement surface 153 and the pivotal pin 14, the plug 161 and the spacer 163 are moved together to press and deform the tightening ring 162, thereby tightly clamping the air valve 12. As such, the pump head 1 is switched to an inflating state (see FIG. 3) from the initial state. By reversely rotating the cam lever 15 to switch the pump head 1 from the inflation state to the initial state, the air valve 12 can be detached from the pump head 1.
Because the distance between the first engagement surface 153 and the pivotal pin 14 is different from the second engagement surface 154 and the pivotal pin 14, rotating the cam lever 15 about the pivotal pin 14 to switch the pump head 1 between the initial state and the inflating state can encounter large impediment force. Further, in order to switch the pump head 1 between the initial state and the inflation state, one hand has to hold the cylindrical body 131, and the other has to operate the cam lever 15. Therefore, it is inconvenient to operate the pump head 1.